1. Field of the Invention
The present invention relates to methods for producing a multi-layer printed wiring board, and particularly, methods of producing a multi-layer printed wiring board by a buildup method using a prepreg.
2. Discussion of the Background
Conventionally, when a prepreg is used for forming an insulating layer of a multi-layer printed wiring board, it is a general practice to layer a prepreg on an inner layer circuit board, and pressurize and heat with a hot press or a vacuum laminating machine one by one. For example, JPA-2003-332740 discloses a method of forming an insulating layer on a circuit board one by one by treating a glass cloth prepreg and a copper foil with a vacuum pressing-type laminating machine. However, in view of the recent preference toward downsized and thinner electronic devices, there is an increasing demand for ultrafine wiring also in a printed wiring board having a multi-layer structure. To meet the need, it is advantageous to form a conductive layer by plating according to a semi-additive method rather than forming a conductive layer with a copper foil. In addition, formation of an insulating layer one by one cannot be said to be a satisfactory method also from the productivity. JP-A-2003-340952 discloses a method of producing a multi-layer printed wiring board using a stage B resin composition sheet with a release film, which is obtained by adhering by lamination of a sheet, wherein a stage B resin composition for additive is adhered to one surface of a release film, on a fiber cloth substrate. While this method enables formation of a conductive layer by plating, a vacuum press apparatus is used for forming an insulating layer and an insulating layer is also formed one by one. Thus, it cannot be said to be a satisfactory method from the productivity. A production method of an insulating layer of a multi-layer printed wiring board using a prepreg, which enables formation of a conductive layer by a semi-additive method without forming the layer one by one has not been put to practical use.